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1968 4v 390 10.5 CR? Pump Gas?

July 25th, 2015, 03:36 PM

Tearing down a 68 Mercury 4v 390 to replace the one in my 62TBird. I believe these are 10.5:1 motors. Can I use same Flattop piston or have to use a dished one to lower CR? Some of you running 10.5 CR still?

Have heard that a larger cam drops CR some anyway and wondering if RV cam will work with the 10.5 CR?

Here are some desktop dyno results posted on FE board using several different cams, but with 9.5 CR instead of 10.5. You have any cam recommendations for torque increase over stock?

I will probably change to Performer or Performer Plus intake primarily for weight reduction (painted Ford intake color). Not sure what to do about exhaust yet...

WerbyFord On cams:

Assuming you have the c1ae-a heads for about 9.5cr, here is what the Gonkulator says - assuming the best 2" glasspacks you can get on the back or equivalent see-thru muffs. With 2" pipe it will not be loud anyway:
Stock 186-186
Torq 382 at 2800
Powr 289 at 4500
2.49 60ft
10.44 at 68.7 1/8 mile
16.14 at 85.5 1/4 mile
8.34 0-60m

Mike, there are many more facets to producing more torque and HP. Huge gains can be made by using aluminum heads and EFI. If you can dissipate heat fast enough and burn high enough octane, 11:1 CR can be used. But let's come down to earth and work with components that are readily available and burn common unleaded pump gasohol.

I assume we're talking about a daily driver. Compression ratio is the result of combustion chamber size, head gasket thickness and type of pistons used. The cam has little to do with it other than valve timing.

EFI atomizes the fuel and it wakes up carbureted engines by producing much more power using the same fuel. Carbs have a hard time hitting the optimum 14.7:1 air to fuel ratio but EFI runs there all the time regardless of temps, altitude, humidity, etc. A hydraulic roller cam will eliminate the need for ZDDP and make cam timing more crisp. - Dave

Comment

Yes, I have seen a couple FI systems that look interesting, but they are expensive and take away from the simplicity of just running a carb, which is a lot easier to fix and trouble-shoot on the side of the road even, if necessary.

I am for sure going to aluminum intake and aluminum heads are not out of the question, though not cheap. Yes, more or less a driver, though maybe leaning restomod with mostly stock appearance, but enhanced mechanicals.

I live out in the country and much of my driving is freeway and longer distances, so not the same as tooling around town to local car shows. If local cruises were the case, I could probably just install 3:30 third member and more or less stock rebuild and call it good enough. But, I like to be able to drive half way across the country, if I have the time.

Since the CM trans will at least need a rebuild too (for reliability sake...), am I better off to put in a C6 from a 69 Galaxie that is sitting in storage? Have read that it is 50 lbs less and better able to deal with a little extra power.. I like having overdrive and have several T85's but want to keep this an automatic trans so the wife can drive it too.

Also hear that another 75 lbs can be dropped with aluminum intake and water pump, although not sure about head weight difference between aluminum and iron. Already have the intake. Ceramic headers from FPA run about $850 they told me. So, it definitely adds up.

Brought the 68 engine to machinist today so they tell me it should be done in about 4 weeks with me doing the assembly. Have assembled several Ford motors before and found all of them easier than early Dodge hemi and Chev 348 that I most recently put together.

Roller cam conversion is not out of the question either, but not sure how that affects torque, since it probably will not see 5000 RPM that often.

I have read quite a few articles that indicate that the cam overlap on some cams bleeds of some of static compression, but not sure how that works out in the real world.

Thanks for your response. Mike

Comment

Yes, I have seen a couple FI systems that look interesting, but they are expensive and take away from the simplicity of just running a carb, which is a lot easier to fix and trouble-shoot on the side of the road even, if necessary.I am for sure going to aluminum intake and aluminum heads are not out of the question, though not cheap. Yes, more or less a driver, though maybe leaning restomod with mostly stock appearance, but enhanced mechanicals.

I live out in the country and much of my driving is freeway and longer distances, so not the same as tooling around town to local car shows. If local cruises were the case, I could probably just install 3:30 third member and more or less stock rebuild and call it good enough. But, I like to be able to drive half way across the country, if I have the time.

Thanks for giving more information regarding your situation. Performance parts are expensive, especially for engines that have been out of production for many decades. Consider the number of EFI systems in service. Not many disabled cars are due to EFI reliability or performance. If you drive long distances, fuel economy must be a major concern. Of all the performance parts out there, EFI delivers the most HP, the best economy and it will pay for itself. Carbs must be run rich to prevent preignition.

Since the CM trans will at least need a rebuild too (for reliability sake...), am I better off to put in a C6 from a 69 Galaxie that is sitting in storage? Have read that it is 50 lbs less and better able to deal with a little extra power.. I like having overdrive and have several T85's but want to keep this an automatic trans so the wife can drive it too.

For your needs the difference between a cruise-o-matic and a C6 is, personal preference. The COM will easily handle your HP with little overhead. The C6 will handle more HP but it taxes more.

Also hear that another 75 lbs can be dropped with aluminum intake and water pump, although not sure about head weight difference between aluminum and iron. Already have the intake. Ceramic headers from FPA run about $850 they told me. So, it definitely adds up.

Brought the 68 engine to machinist today so they tell me it should be done in about 4 weeks with me doing the assembly. Have assembled several Ford motors before and found all of them easier than early Dodge hemi and Chev 348 that I most recently put together.

Roller cam conversion is not out of the question either, but not sure how that affects torque, since it probably will not see 5000 RPM that often.

I have read quite a few articles that indicate that the cam overlap on some cams bleeds of some of static compression, but not sure how that works out in the real world.

Thanks for your response. Mike

Since you have built Ford engines, you must know they are drastically different and more expensive than Chevy. I've seen Chevy builders give up on an FE. Ford made about fifty different sets of intake and heads so make sure your set is compatible. Camshafts determine the torque curve. Overlap determines the amount of scavenging, again, for more HP but at the cost of fuel economy. - Dave

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